Can't see network computer with 2 Routers - HELP

Really need help guys.

I have a network we setup a while back with a DSL line which uses a static IP and goes through an old router. From there we route it to a switch which all the computers in the office are on and they connect to a fileserver which is in the router room. It's just running windows XP and we shared a folder on it and all it does is share a quickbooks file that they use.

the IP range for all these computers is 192.168.0.1 to whatever

We added a wireless router where we just plugged it into the switch and the other end into the WAN line of the new router. I checked one laptop that has WIFI and it connects and we get internet but we are not able to hit the fileserver. It keeps saying we don't have access. I am able to PING the actual ip of the server but when i try to get onto the network it says we do not have access to it. I set the DMZ on the older router to the IP of the file server but that didn't do anything. The new router IP range is 192.168.1.1 to whatever.

ANy help would be greatly appreciated. I really need to get the wireless computers to be able to see the server as well through the setup we have now.

Thanks